Now, through mutual communication, A and B want to set up a session key that is used to keep this last data secure. Our new protocol is illustrated in Figure 2. (1) First, the short-lived private key of vehicle A is randomly selected and its volatile public key is defined as. Then A sends to vehicle B:(2)Meanwhile, a random value is selected as the volatile private key of vehicle B. Then, B also calculates as a short-lived public key. B transmits to A:(3)After receiving messages from B, A can calculate and. This allows A to calculate the session key. 4. In the same way, vehicle B, if B receives the data sent by A, can calculate the session key and. B also calculates. .